Physics Tip Sheet #12 - May 8, 2002

Researchers formed a square array of copper cylinders and found that they form an acoustic band-gap which will completely block a certain range of frequencies. A variation on the idea could be used to make lightweight sonic insulation.

2) Should life be common in the universe? C. H. Lineweaver, T M. Davis arXiv preprint server

An argument sometimes used for the existence of life elsewhere in the universe is "if life evolved rapidly, as it did on Earth, then life must be common". The authors look at the assumptions inherent in this argument and conclude that the probability of biogenesis on Earth-like planets older than one billion years is greater than 1 in 3. This gives a value to one relevant factor in the extraterrestrial life argument but does not mean that life is necessarily common in the universe.

A new technique has produced single intense light pulses shorter then 4 femtoseconds (1 femtosecond=10^-15 seconds). The pulses are created using a technique called molecular phase modulation in which an initial pulse excites a molecule into some form of vibration or rotation. Then a second pulse sees the molecule's vibration or rotation as a change in refractive index, like a molecular-sized lens, which effectively focuses it to the ultra-short duration observed.

An experimental study has shown that the phonons (sound wave vibrations) in DNA molecules are characteristic of particular DNA sequences and can be observed using spectroscopic techniques. The authors examined the sequences, structures and dynamics of herring and salmon DNA sodium salts and concluded that the technique has potential application for obtaining DNA signatures.

When light refracts form one substance to another, it always bends one way. However, recent results suggested that certain (left-handed) materials could make light bend the other way. One of the possible implications of the work is that a perfect lens could be made. The result has stirred up controversy with new papers suggesting that light can only bend the usual way and even if they could bend light backwards, left-handed materials would not make a perfect lens.

Microscopic pinholes may soon allow the one-by-one transfer of photons in a way that mimics the process of a Coulomb blockade of electrons in which electrons line up on quantum dots to be released individually. The presence of one electron on a dot stops other electrons from joining it and puts a limit on the rate electrons can flow through the dot. In an optical equivalent, the authors covered a glass plate with a gold film containing cracks and gaps. They then filled the gaps with a transparent polymer. By looking at the light coming through individual gaps, they observed a maximum in the amount of light that could pass through, just as if photons in the gaps were preventing further photons from coming through.